Fur or wool felt hats start out as a cone that is roughly shaped to a raw body by stretching. It is then further processed in a labor-intensive sequence of steps to the familiar hat shape. Two theories of the formation of felt itself, the intertwining and plastic theories, seem to be the basis also for the later steps of hat shaping. According to the intertwining theory, the fibers are mechanically manipulated and forced among each other. The plastic theory holds that the fur or wool fibers become temporarily plastic at elevated temperatures. The hand process involves blocking the crown and flanging the brim.
Skilled crafts people using simple fixtures or machines can perform these operations. Crown stretching is done on a fixture which has a frame over which the rough felt cone is placed. Metal fingers press the felt at the tip between frame members thereby stretching it. The brim stretcher also uses metal fingers to grip the brim to stretch it to shape. The hat is then roughly blocked into shape by wetting and then pulling it over a wooden block. The final blocking steps for final size are done with the aid of steam and an iron. The hat form is finally finished on a hand-carved block that produces the final style or "character" of the shape.
More sophisticated machines for automating some of the steps in hat making have been around for over a hundred years. Starting with a raw felt body, one process involves forming the brim flange by stretching this region using metal fingers before applying steam. The body with the formed brim is then dried on a rack. The dry hat is then put into a female mold and a rubber bladder is inserted in the crown portion and expanded by hydraulic pressure so that the crown is expanded into intimate contact with the female mold. Michelangnoli, a company in Signa, Italy, makes an automatic machine based on this hydraulic principle. Other machines, such as automatic stampers, are used to achieve a final shape to the hat form.